In the administration of an intravenous solution, the control of its flow rate to the patient represents a critically important task. Allowed to become excessive, the intravenous solution results in the thinning of the patient's blood in a portion of his vascular system. Tissues depending upon the nutrients and biochemicals entrained in the blood can suffer serious consequences upon the arrival of blood overly diluted with the administered solution.
In U.S. patent application Ser. No. 732,946, R. Scott Turner et al. now U.S. Pat. No. 4,121,584, provides a significant advance in maintaining the flow rate of an intravenous solution at a safe level. One component of Turner et al.'s apparatus takes the form of a metering unit which constitutes part of the flow path followed by the I.V. solution. The metering unit has a metering chamber with a known volume. It also has an inlet and an outlet with a valving device associated with each. Since the solution contacts the metering unit as it flows through it, each unit finds use with a single administering set and is discarded with it.
As the other component of their equipment, Turner et al. provide a controller for sequentially opening and closing the inlet and outlet valves in the metering unit. When the inlet opens, the metering chamber then ingests a predetermined amount of the intravenous solution. The controller then closes the inlet and opens the outlet. This permits the known volume of fluid to flow to the patient. The controller subsequently shuts the outlet and repeats the cycle at a frequency that will deliver the appropriate amount of solution. The metering unit and the controller have minimal weight and may receive support simply from their connection to the intravenous administering set. Since the controller merely opens and closes two valves, it requires minimal electricity and may operate from the current supplied by a battery.
Scott F. Garrett et al., in the patent application "Casette for Use with I.V. Infusion Controller," referenced above, introduce drastic improvements into a casette included as part of the flow path of the intravenous administering equipment. They utilize a section of elastomeric stretchable membrane to form part of a metering chamber having a predetermined volume. The membrane also constitutes part of the inlet and the outlet which passes the fluid into and out of the metering chamber.
A base section of plastic also forms part of the inlet, the outlet, and the metering chamber. A cover slip of plastic then sandwiches the membrane between it and the base piece of plastic. It also limits the expansion of the elastomeric membrane to provide a metering chamber of a known volume. The controller in Garrett et al.'s apparatus need only deform the elastomeric membrane until it makes appropriate contact with the valve seat formed in the base section of plastic.
Providing further improvements to the controller as well as the casette portend the close cooperation of the two in maintaining a safe flow rate of solution to the patient. It can also provide a safeguard even against the slight possibility of a malfunction occurring in the controller.